3S6 Mr. T. Bentham 



on some 



ends than those of other fish, and measure roughly 12-13 /j. 

 in length by about 9 ll in breadth. About the centre of the 

 cell-body is a comparatively small nucleus, staining dark 

 blue. Besides these elements are a certain number of 

 erythroblasts or immature red-cells. These are characterized 

 by being slightly smaller and more rounded than the erythro- 

 cytes, and by staining blue iustead of, as in erythrocytes, 

 pink by the Romanowsky method. The nuclei of these 

 cells are comparatively larger than those of erythrocytes, 

 but in no way approach the size attained by those in birds ; 

 hence they cannot possibly be confused with medium lympho- 

 cytes. 



The leucocytes, if we include thrombocytes, are of six 

 different kinds — small, medium, and large lymphocytes, 

 eosinophils, mast-cells, and the thrombocytes above men- 

 tioned. 



The lymphocytes are in smear preparations all rounded in 

 shape, with a single nucleus which is always excentric in 

 position in the cytoplasm. In the small and medium forms 

 the nucleus occupies nearly the whole of the cell, there 

 being merely a thin ring of cytoplasm round the edge. In 

 the large forms the nucleus is relatively small, being in 

 diameter not more than one-third of the diameter of the 

 whole cell. The small forms measure only about 8 /j, in 

 diameter, the medium about 12 //., and the large from 18-20 fi. 

 Iu all, the cytoplasm stains pale blue, the nucleus purple, by 

 the Romanowsky method, and they constitute about 15 °/ of 

 the cellular elements of the blood. 



Eosinophils are small in the mackerel compared with 

 those of other groups. They are rounded in shape and 

 measure about 8 /x in diameter, have a single excentrically 

 placed nucleus, and their acidophil granules are rounded and 

 occupy a fairly large space of cytoplasm on one side of the 

 nucleus. They are only slightly more numerous than the 

 next type. .Mast-cells are slightly larger than eosinophils. 

 They stain a pale blue and do not seem to possess any 

 nucleus. In place of this there are scattered about in the 

 cytoplasm a moderate number of rounded, purplish, deeply 

 staining granules which vary considerably in size. They 

 occur very rarely in films, there being about one or two in 

 each smear. Thrombocytes in fish are fairly constant in 

 shape, aud are to be recognized by both their elongated 

 fusiform shape and their elongated centrally placed nucleus. 



They are in length about 12 fx, but only about 5 /a in 

 breadth at their widest part. The nucleus measures about 

 7 fju by 5 fj,, so that at its widest part it touches the edge of the 



